Pleated blinds usually consist of a head rail and a bottom rail and one or more cords which are used to raise or lower the bottom rail with respect to the head rail. An expandable and collapsible pleated shade is arranged between the head rail and the bottom rail so as to expand or collapse along predetermined fold lines when the bottom rail is raised or lowered. The predetermined fold lines usually lie parallel to the head rail and bottom rail. The pleats of the shade are usually manufactured to be equal size within normal manufacturing tolerances.
During normal use of the blind, each pleat carries the cumulative weight of every pleat beneath it, other than those which are resting on the bottom rail. The greater the vertical dimension of the blind, the greater the weight that the higher pleats carry. A consequence of this is that the uniform appearance of equally spaced pleats is lost, because the load on each pleat causes the pleat to creep and open up the angle of its fold. Eventually, the apparent distance between pleats is noticeably greater at the top of the blind than it is at the bottom. The blind can be described as "sagging". For free hanging blinds installed vertically to rectangular windows, this sagging effect does little more than alter the appearance of the blind as described. However, an increasingly popular use for pleated blinds is in conservatory roofs, many of the window shapes of which are not rectangular. The problem of sagging of, for example, a triangular blind manifests itself as a progressively curving and tapering gap between the edge of the blind and the window frame. In these circumstances, the blind is no longer covering the whole of the window area and this is clearly undesirable.
The problem of blind sagging has been addressed and it is known to take remedial steps by mechanically fixing the pleats in their desired position. This is often done by supporting them from above. The simplest way of achieving this is to sew a very fine thread or monofilament from pleat to pleat, ensuring that the length of thread of monofilament between adjacent pleats is uniform. However, this method is a very slow and labour intensive one.
Another method which has been proposed involves attaching a light ribbon to the back of equally spaced pleats, pleat by pleat, by use of what is known as a "Kimble tag" and gun. Kimble tags are commonly used to attach labels to clothes. The disadvantage of this method is that the entire blind has to be spread out on a rigid corrugated former made, for example, from 90.degree. angle aluminium. This pre-spaces the pleats before the ribbon is attached. This is both space and time consuming.
A third method involves passing a cord from the head rail to the bottom rail through apertures in each of the pleats--this being done commonly to maintain the blind in the desired vertical plane--and then to provide a second cord running down the back of the shade and provided with loops at regular intervals. The cord which passes through apertures in the pleats also passes through the loops of the second cord and these loops prevent their respective pleats from sagging beyond a pre-determined position. Again, the manufacture of this type of blind is time consuming and costly in terms of labour.